PharmacognosyPHR 113 / Lecture 4

Evaluation of crude drugs

Drug evaluation may be defined as the determination of identity, purityand quality of a drug.

• Identity – identification of biological source.

• Quality – quantity of the active constituents.

• Purity – presence or absence of foreign materials.

Methods of Drug Evaluation

The evaluation of a drug is drug done by studying its various properties. The various properties are:

• Organoleptic property• Microscopic property• Biological property• Chemical property• Physical property

Organoleptic (Morphological) Evaluation

• Drug evaluation by means of our organs of sense such as odor, color,taste and texture.

• Study of morphology and other sensory characters.

• Study of Gross Morphology• Visual examination of drug.

Organoleptic (Morphological) Evaluation

• Barks - all the tissues in a woody stem• Leaves –shape, margin, base, apex and venation of leaves

Study of Sensory Characters

• Color• Odor• Taste• Texture

Study of Sensory Characters

Color: • Some drugs are green in color when dried in shade.• But they become pale and bleached when dried in sunlight.• Terminalia chebula - Fresh and Dried

Odor: • The odor of the drug may be either dissimilar or similar.• The terms used for the drugs are aromatic, spicy etc.• Mentha, clove are some of the examples for the drugs which have a

distinct odor.

Study of Sensory Characters

Taste:• The drugs may be evaluated by taste also.• The taste may be saline, sour, salty, sweet, bitter etc.• The substances without taste are regarded as tasteless.

Texture:Sometimes drugs can be exanimated by their consistency, texture and nature of fracture.

Microscopic or Anatomical Evaluation

Used to identify organized drugs by their known histological characters.

Before examination through a microscope the material must besuitably prepared.

This can be done by powdering, cutting thin sections of the drug

Microscope can also be used for a quantitative evaluation of drugs andadulterated powders.

Microscopic or Anatomical Evaluation

This is done by counting a specific histological feature such as: • Stomatal Number• Stomatal Index• Vein-islet Number• Palisade Ratio• Quantitative Microscopy• Refractive Index

Microscopic or Anatomical Evaluation

Stomatal Number: for identification of a leaf drugStomatal Number = Average number of stomata present per squaremillimeter of the epidermisStomatal number is constant for a particular speciesExample: Datura – 141 (upper epidermis)

Stomatal Index:Stomatal Index = proportion of the number of stomata to the totalnumber of epidermal cellsStomatal number is constant for a given species.Example: Atropa – 20.0-23.0 (lower epidermis)

Microscopic or Anatomical Evaluation

Vein-islet Number:Vein-islet number = the number of vein-islets per sq.mm. of leafsurface.• It is constant for a given species of the plant.• Example: Cassia senna (26).

Palisade ratio:Average number of palisade cells underneath one epidermal cell

Example: Atropa belladonna – 06-10

Physical Evaluation

• Moisture Content• Viscosity• Melting point• Optical Rotation• Refractive Index• Ash Content• Extractive values• Volatile oil Content• Rf Values

Physical Evaluation

Moisture Content:Moisture content can be determined by heating the drug at 150⁰C in anoven to a constant weight and calculating the loss of weight.

Viscosity:It is used as a means of standardizing liquid drugs.Example: Liquid paraffin – less than 64 centistokes.

Melting Point:It is one of the parameters to judge the purity of crude drugs.Example: Coca butter (30⁰ - 33⁰C)

Physical Evaluation

Optical Rotation: For determination of chirality of active compounds

Refractive Index: It is measured by means of refractometer.Example: Arachis oil - 1.4678-1.4698

Ash Content:Ash simply represents the inorganic salts naturally occurring in drug or adhering to it or deliberately added to it as a form of adulteration.Example: Ashoka – 11.00

Ginger – 6.00

Physical Evaluation

Extractive values: Water, alcohol or ether soluble extractive values aredetermined for evaluation of such drugs.Example: Water soluble extracts like Aloe vera

Alcohol soluble like Ginger

Volatile oil content: Crude drugs are standardized on the basis of theirvolatile oil contents.

Rf / Retardation Factor Values: for both qualitative and quantitativeevaluation of drugs.

Chemical Evaluation

Determination of the active constituent in a drug by chemical tests isreferred to as chemical evaluation.

For example:Instrumental methods: colorimetry, spectrophotometryChemical Constants: acid value, iodine value and ester value

Biological Evaluation

In this method, the response produced by the test drug on a livingsystem is compared with that of the standard preparation.

Example: Cardiac glycosides arte evaluated by this method on cats,frogs or pigeons.

Thank you

Mohammad Ahad A Khan, PhDAssistant Professor, Department of Pharmaceutical SciencesNorth South University, Bangladesh Room: SAC 1013email: mohammad.khan03@northsouth.eduCell: +880 17 0386 4707